Add flags to allow dynamic loader to find Postgres sharable libraries without

 having to modify the system-wide library database.

src/makefiles/Makefile.linux

 ifdef LINUX_ELF
-LDFLAGS+= -rdynamic
+LDFLAGS+= -rdynamic -Wl,-rpath -Wl,$(DESTDIR)$(LIBDIR)
 endif
 MK_NO_LORDER= true